Conventionally, in a generator disclosed in JP-A-54-116610 or JP-A-6-86517, as shown in FIG. 20, a rotating shaft 1 penetrates a bracket 2 via a bearing 3, the bracket 2 serving as an outer casing. A field winding 5 is provided on an outer periphery of a yoke 4 which is fit and fix to the rotating shaft 1, and claw-shaped magnetic poles 6 and 7 are provided so as to alternately protrude from right and left sides of the field winding 5, whereby a rotor is formed as a whole. Meanwhile, stator windings 8 are provided on the bracket 2 so as to face the claw-shaped magnetic poles 6 and 7. Electric power to the field windings 5 is supplied slidably via a slip ring 9.
According to the above configuration, when a direct current is supplied to the field winding 5 via the slip ring 9 so that an N-pole is generated on the right side of the field winding 5 as viewed in the figure and an S-pole is generated on the left side of the field windings 5 as viewed in the figure, an N-pole is induced on the claw-shaped magnetic pole 6 protruding from the right side while an S-pole is induced on the claw-shaped magnetic pole 7 protruding from the left side. Thus, a plurality of N-poles and a plurality of S-poles can be generated alternately on an outer circumferential side of the rotor along a circumferential direction thereof.
However, the field winding 5 is formed as a part of the rotor, and an electric power supply to the field winding 5 which moves rotationally needs to be performed via the slip ring 9 by a sliding-contact. Thus, a structure becomes complex. Also, there are problems such as a reduction of life due to a contact wear at the slip ring 9, and a destabilization of a power supply due to a destabilization of the sliding-contact at the slip ring 9.
Patent Document 1: JP-A-54-116610
Patent Document 2: JP-A-6-86517